Array temperature sensing method and system

ABSTRACT

Methods and apparatus enable monitoring conditions in a well-bore using multiple cane-based sensors. The apparatus includes an array of cane-based Bragg grating sensors located in a single conduit for use in the well-bore. For some embodiments, each sensor is located at a different linear location along the conduit allowing for increased monitoring locations along the conduit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application a continuation of co-pending U.S. patent applicationSer. No. 11/957,181, filed Dec. 14, 2007, which is a continuation ofco-pending U.S. patent application Ser. No. 11/468,646, filed Aug. 30,2006. Each of the aforementioned related patent applications is hereinincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention generally relate to apparatus and methodsof measuring conditions in a well-bore.

2. Description of the Related Art

Distributed Temperature Sensing (DTS) enables monitoring temperaturealong the length of a well. A DTS system utilizes an optical waveguide,such as an optical fiber, as a temperature sensor. In a typical DTSsystem, a laser or other light source at the surface of the welltransmits a pulse of light into a fiber optic cable installed along thelength of the well. Due to interactions with molecular vibrations withinglass of the fiber, a portion of the light is scattered back towards thesurface. A processor at the surface analyzes the light as it is sentback. The processor then determines the temperature at various depthswithin the well, based on the reflected light.

A problem with DTS systems is that the signal reflected back to theprocessor is weak and can be difficult to read. This problem isespecially true for long waveguides in deep wells. Therefore, the weaksignal makes it difficult to accurately determine the temperature indeep well-bores.

Utilizing an Array Temperature Sensing system (ATS) overcomes the weaksignal of the DTS system. In the ATS system, several Bragg gratings areplaced in a waveguide, such as a fiber. The gratings can be at anydesired location along the waveguide. Advantageously, a reflected signalfrom the grating is greater than that of the DTS system.

A major challenge to the use of an ATS system involves the packaging ofthe Bragg gratings such that they are responsive to the temperature oftheir surroundings but are free from, or insensitive to, strain changesover their lifetime. The effects of these strain changes are generallyindistinguishable from those of changes in temperature and cause errorsin the temperature measurement.

DTS measurement is also sensitive to changes in the loss and refractiveindex of the optical fiber being interrogated, while the gratings of theATS system are sensitive to changes in the refractive index and physicaldimension of the fiber. In many cases, such changes happen over thelifetime of the system. For example, production fluids and gases,particularly hydrogen, in a well-bore can cause significant increases inthe fiber loss and refractive index of glass optical fibers. The ingressof production fluids, e.g., water, can cause swelling of the glassoptical fibers which changes the measured wavelength and hence measuredtemperature of the Bragg gratings in the ATS system.

Therefore, there exists a need for an improved ATS system that reflectsa stronger signal than a DTS system and eliminates or at least reducesadverse effects of changes in strain over the system lifetime. A furtherneed exists for methods and assemblies to provide the ATS system that isprotected from the ingress of fluids and gases.

SUMMARY OF THE INVENTION

Embodiments of the invention generally relate to methods and apparatusthat enable monitoring conditions in a well-bore using multiplecane-based sensors. The apparatus includes an array of cane-based Bragggrating sensors located in a single conduit for use in the well-bore.For some embodiments, each sensor is located at a different linearlocation along the conduit allowing for increased monitoring locationsalong the conduit.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a partial sectional view of a well-bore having a conduit withmultiple Array Temperature Sensing sections, according to embodiments ofthe invention.

FIG. 2 is a view of an array of temperature sensors provided at enlargedouter diameter portions of a waveguide relative to interconnecting fiberportions of the waveguide between the enlarged outer diameter portions.

FIG. 3 is a sectional view of the array of temperature sensors disposedin a protective tube.

FIG. 4 is a sectional view of the array of temperature sensors disposedin the protective tube and an armor layer surrounding the protectivetube.

FIG. 5 is a sectional view of a temperature sensor mounted in a fixturewithin a tube.

FIGS. 6A through 6F illustrate successive stages of a procedure forproviding a segmented ATS assembly that can, for example, form at leastpart of the conduit shown in FIG. 1 implementing aspects of theinvention illustrated in FIGS. 2-5.

FIG. 7 is a sectional view of a feed-through for disposal along an ATSassembly.

DETAILED DESCRIPTION

Embodiments of the invention generally relate to methods and assembliesfor monitoring one or more parameters at multiple discrete locations ina well-bore. For example, temperature can be measured using multiplesensor arrays on multiple waveguides enclosed in a single conduit.According to some embodiments, a large diameter optical waveguidesection having a reflective grating disposed therein defines anindividual sensing element or sensor, which is spaced from other sensorswithin an array of sensors by interconnecting lengths of waveguide, suchas optical fiber, that have relatively smaller outer diameters than thesensors.

As used herein, the term “large diameter optical waveguide” (“cane”)refers to any optical waveguide having at least one core surrounded by acladding that has an outer diameter of 0.3 millimeters (mm) or larger,for example, about 4.0 mm or more. The large diameter optical waveguidepreferably includes silica glass (SiO₂) based material havingappropriate dopants to allow light to propagate in either directionthrough the core. Other materials for the large diameter opticalwaveguide may be used, such as phosphate, aluminosilicate, borosilicate,fluoride glasses or other glasses, or plastic.

Furthermore, the large diameter optical waveguide is thicker andsturdier because of a substantial amount of cladding than standard fiberthat has an outer diameter of, for example, 125 microns. In other words,a clad-to-core diameter ratio of the large diameter optical waveguide islarge (e.g., ranging from about 30 to 1 to 300 to 1) when compared to astandard optical fiber clad-to-core ratio of approximately 12 to 1.Therefore, a length-to-diameter aspect ratio of the large diameteroptical waveguide causes the large diameter optical waveguide to resistbuckling in the event the sensor is placed in axial compression. Thisrigidity of the large diameter optical waveguide substantially avertssusceptibility of the large diameter optical waveguide to breakage andlosses caused by bending. Additionally, the core of the large diameteroptical waveguide can have an outer diameter of about 7 to 12 micronssuch that it propagates only a single spatial mode at or above thecutoff wavelength and a few (e.g., six or less) spatial modes below thecutoff wavelength. For example, the core for single spatial modepropagation can have a substantially circular transverse cross-sectionalshape with a diameter less than about 12.5 microns, depending on awavelength of light.

FIG. 1 illustrates a cross-sectional view of a well-bore 100 having aconduit 102 equipped for sensing downhole conditions. As shown, theconduit 102 includes a first waveguide 104A, a second waveguide 104B anda third waveguide 104C that are all suitable for transmitting opticalsignals. The conduit 102 can be any tubular member for containing thewaveguides 104A-C and can include components (not shown) such asarmoring, a metal tube, a buffer, etc. While illustrated as having threewaveguides, any number of waveguides can be utilized within the conduit102. Each of the waveguides 104A-C includes a respective first array106A, second array 106B and third array 106C located along a lengththereof.

Each of the arrays 106A-C includes sensors 108A-N, 110A-N, 112A-N,respectively. The number of sensors on each of the waveguides 104A-C candepend on the frequency of light reflected back at each of the sensors108A-N, 110A-N, 112A-N. The sensors 108A-N, 110A-N, 112A-N can be spacedat any desired interval in the arrays 106A-C, which can be located atany depth. For example, the sensors 108A-N, 110A-N, 112A-N can be spacedbetween about 0.5 meters to approximately 1.0 kilometers apart withineach of the arrays 106A-C. In some embodiments, the arrays 106A-C are inseries, one after another, thus the first array 106A is followed by thesecond array 106B so that a long length of the well-bore is monitored bythe conduit 102. The conduit 102 with the arrays 106A-C along with thesensors 108A-N, 110A-N, 112A-N can incorporate any of the variousfeatures and aspects described in further detail hereinafter relating tocorresponding elements and assembly techniques.

FIG. 2 shows an array 404 of temperature sensors including a firsttemperature sensor 400A, a second temperature sensor 400B and a thirdtemperature sensor 400N. The sensors 400A-N enable a plurality ofdiscrete point temperature measurements at each location of the sensors400A-N. Enlarged outer diameter portions along a waveguide define largediameter optical waveguide sections where the sensors 400A-N areprovided. Interconnecting fiber portions 402A-N of the waveguideoptically connect between ends of the sensors 400A-N such that thesensors 400A-N are spaced from one another along a length of the array404. With this arrangement, the interconnecting fiber portions 402A-Nalong with the sensors 400A-N establish the waveguide, which iscontinuous across the length of the array 404. Further, the sensors400A-N have a relatively larger outer diameter compared to an outerdiameter of the interconnecting fiber portions 402A-N. As previouslydescribed, the large diameter optical waveguide sections where thesensors 400A-N are located provide limited sensitivity to strain effectsdue to increased cross-sectional area.

With reference to the first sensor 400A, each of the sensors 400A-Nincludes a reflective grating 406, such as a Bragg grating, disposedtherein to permit measuring temperature based on interrogation of lightsignals reflected from the grating 406. Additionally, theinterconnecting fiber portion 402A splices to a mating end 401 of thefirst sensor 400A where the large diameter optical waveguide section ismachined to an outer diameter substantially matching an outer diameterof the interconnecting fiber portion 402A. Machining the mating end 401of the first sensor 400A enables fusion splicing between the largediameter optical waveguide section and the interconnecting fiber portion402A. Such fusion splicing can be automated with a fast splicingapparatus commonly used in the art for splicing optical fibers. It isalso possible to check the yield strength of the splice with commonlyused optical fiber test apparatus. See, U.S. Publication No.2004/0165841, entitled “Large Diameter Optical Waveguide Splice,” whichis herein incorporated by reference in its entirety. An excess length ofthe interconnecting fiber portion 402A (i.e., overstuff when the array404 is within a cable or conduit) prevents the straining of the sensorelements by eliminating tension on the interconnecting waveguide.

For some embodiments, machining the large diameter optical waveguidesection forms the mating end 401 with a conical taper to give a highstrength transition between the first sensor 400A and theinterconnecting fiber portion 402A. The mating end 401 can, for someembodiments, include a length of optical fiber tail spliced to where thelarge diameter optical waveguide section is machined such that the firstsensor 400A with the mating end 401 can be a subassembly manufacturedoffline and the in-line fiber-to-fiber splicing between the mating end401 of the first sensor 400A and the interconnecting fiber portion 402Acan be performed with improved quickness, ease and accuracy. See, U.S.Publication No. 2004/0165834, entitled “Low-Loss Large-DiameterPigtail,” which is herein incorporated by reference in its entirety. Insome embodiments, the first sensor 400A can be metal plated to provideprotection from ingress of fluids and gases by, for example, using avacuum deposition process on the large diameter optical waveguidesection. As an example, the first sensor 400A can be metal plated withgold, which has low hydrogen permeability and permittivity.

FIG. 3 illustrates the array 404 of temperature sensors disposed in aprotective tube 500. The tube 500 further protects the array 404 from asurrounding environment by inhibiting mechanical disruption, fluidingress and/or gas ingress. For some embodiments, the tube 500 can beplated to further hinder ingress of gases into an interior where thearray 404 of temperature sensors are disposed.

In operation, the array 404 of temperature sensors can be pulled intothe tube 500 after several of the sensors 400A-N have been connectedtogether by the interconnecting fiber portions 402A-N. If it is desiredto avoid pulling a substantial length of the array 404 of temperaturesensors into the tube 500, the tube 500 can be assembled in sectionsalong with the array 404 of temperature sensors. With this concurrentassembly, sections of the tube 500 are successively positioned over oneor more corresponding pairs of the sensors 400A-N and theinterconnecting fiber portions 402A-N as the length of the array 404 oftemperature sensors increases during fabrication.

FIG. 4 shows the array of temperature sensors 404 disposed in theprotective tube 500 and an armor layer 600 surrounding the protectivetube 500. The armor layer 600 provides additional mechanical protectionand can be plated to improve blocking of gases. For some embodiments,the armor layer 600 is plated with about 10.0 microns thickness of tin.The protective tube 500 protects the array of temperature sensors 404during the process of adding the armor layer 600. For some embodiments,the protective layer includes a further encapsulation layer such asSantopreneTM' Additionally, cross section of the armor layer 600 candefine a desired form having a square profile, a flat-pack profile orround profile.

FIG. 5 illustrates the first sensor 400A mounted in a fixture 700 withinreceiving tubing 702. The receiving tubing 702 can be similar to theprotective tube 500 shown in FIG. 4 and can also be surrounded by anarmor layer. In practice, the fixture 700 can be added to the firstsensor 400A as two pieces after assembly of the first sensor 400A intoan array 404 of temperature sensors or fed onto the array 404 oftemperature sensors during integration of the first sensor 400A into thearray 404 of temperature sensors. Regardless of the process for addingthe fixture 700 prior to disposing the array 404 of temperature sensorsin the tubing 702, the first sensor 400A can be affixed in the fixture700 by, for example, adhesives or curable polymers. Further, the fixture700 can also be fixed within the tubing 702 such as with threads, aninterference fit or a weld.

Mounting the first sensor 400A within the fixture 700 can therefore fixa location of the first sensor 400A in a radial direction within thetubing 702 and, if desired, longitudinally within the tubing 702. Forsome embodiments, the fixture 700 can be made of aluminum or Vespel®.Additionally, a material of the fixture 700 and the tubing 702 adjacentthe fixture 700 can be thermally conductive to give a direct thermalpath between an external environment and the first sensor 400A

FIGS. 6A through 6F show successive stages of a procedure for providinga segmented ATS assembly that can, for example, form at least part ofthe conduit 102 shown in FIG. 1. Accordingly, the same referencecharacters identify like elements in FIG. 1 and FIGS. 6A through 6F.Segmentation occurs with this procedure due to creation of repeatingdivisions along the conduit 102 where at least part of the conduit 102is cut in two at each of the sensors 108A-N, 110A-N, 112A-N as exemplaryshown with respect to incorporation of a first sensor 108A in FIGS. 6Athrough 6F. Because the configuration of each of the sensors 108A-108N,110A-N, and 112A-N can be substantially the same, only the first sensor108A is shown and described in detail.

FIG. 6A illustrates a detailed cross-section of an initial preparationto integrate the first sensor 108A. Construction of the first sensor108A begins by providing the waveguides 104A-C in a tube 300 that can beconstructed of metal (e.g., a fiber in metal tube, “FIMT”) or anymaterial suitable for use in a desired application such as a well-boreapplication. Cutting out and removing a section of the tube 300 exposesthe waveguides 104A-C. The waveguides 104A-C extend from first andsecond ends 301, 302 of the tube 300 and are cut leaving portions of thewaveguides 104A-C exposed at the ends 301, 302.

As shown in FIG. 6B, assembly of the first sensor 108A progresses byplacing first and second outer tubing 208, 209 respectively over thefirst and second ends 301, 302 of the tube 300. A tubular insert 206with a fixture or mount 202 attached inside the tubular insert 206 isplaced within the second outer tubing 209; however, the tubular insert206 can alternatively be placed within the first outer tubing 208. Forsome embodiments, the tubular insert 206 includes a steel tubular memberthat is tin plated. The outer tubing 208, 209 has an inner diameterlarger than the outer diameter of the tubular insert 206 and the tubing300. In some embodiments, the outer tubing 208, 209 include steeltubular members that are tin plated. The waveguides 104A-C extendthrough the mount 202.

FIG. 6C illustrates the mount 202 in place and the second and thirdwaveguides 104B, 104C spliced back together where previously cut. Forsome embodiments, the splices 204 are protected by polymide tubesinjected with an ultraviolet or a thermally set polymer such as Sylgard182® thermal cure encapsulant. The splices 204 allow the second andthird waveguides 104B, 104C to pass light freely across where the firstsensor 108A is located.

Additionally, a large diameter waveguide 200 having a Bragg gratingdisposed therein is spliced into the first waveguide 104A. The largediameter waveguide 200 can be metal plated for extra protection. Forsome embodiments, the large diameter waveguide 200 is gold plated butcan also be tin plated, carbon coated, or outer surface covered by othersuitable low permeability material. As described above with reference tothe array 404 of temperature sensors and the first temperature sensor400A in FIG. 2, this configuration for the large diameter waveguide 200with the Bragg grating enables the first sensor 108A to be responsive totemperature. The large diameter waveguide 200 is interrogated with lightpassing through the first sensor 108A and connects the first sensor 108Aalong the first waveguide 104A, which is relatively smaller in outerdiameter than the large diameter waveguide 200.

As shown in FIG. 6D, the large diameter waveguide 200 is next insertedinto the mount 202. The large diameter waveguide 200 and/or thewaveguides 104A-C can then be secured in the mount 202. For example, themount 202 can be filled with Sylgard 182® silicone encapsulant and thencured thermally such that the mount 202 holds the waveguides 200, 104A-Cin place.

FIG. 6E illustrates the first and second outer tubing 208, 209 slidtogether over the tubular insert 206 during assembly of the first sensor108A. As shown, the first and second outer tubing 208, 209 now enclosethe waveguides 104A-C along where the section of the tube 300 wasremoved. With the first and second outer tubing 208, 209 in position,the outer tubing 208, 209 are secured to the tube 300 and one anotherand/or the tubular insert 206. For some embodiments, this securingoccurs by crimping the outer tubing 208, 209 to one or both the tubularinsert 206 and the tube 300. Additionally, orbital welds, laser welds orsolder joints can secure and/or seal an interior area enclosed at thefirst sensor 108A.

FIG. 6F shows the first sensor 108A upon completion of assembly. Anarmoring 210 is placed around the first and second outer tubing 208, 209at the first sensor 108A. The armoring 210 provides corrosion resistanceand mechanical protection to the outer tubing 208, 209. Between each ofthe sensors 108A-N, 110A-N and 112A-N, the waveguides 104A-C can besurrounded by the tube 300 and/or the armoring 210, or any othermaterial for protecting the waveguides 104A-C.

FIG. 9 illustrates a feed-through 900 that can be disposed along theconduit 102 (shown in FIG. 1) to block fluids and gasses thatpotentially propagate along a first inner tubing 909, which can be alength of FIMT used to reach the sensors 108A-N, 110A-N and 112A-N orprovide the interconnection between the sensors 108A-N, 110A-N and112A-N. The waveguides 104A-C can be soldered into the feed-through 900,which can be welded or soldered into the first inner tubing 909. Thefeed-through 900 is adapted to connect to a second inner tubing 908 onone end and the first inner tubing 909 on the other end. Thefeed-through 900 can be arranged to reduce or enlarge the diameter ofthe second inner tubing 908 relative to the first inner tubing 909 toalter an outer diameter of the conduit 102 as required for specificapplications. For some embodiments, the feed-through 900 is gold platedKovar™.

Referring back to FIG. 1, lowering the conduit 102 into the well-bore100 positions all the sensors 108A-N, 110A-N, 112A-N incorporated intothe conduit 102 at desired locations. The use of multiple waveguides,having multiple arrays allows for the monitoring of a large area of thewell-bore, while only having to run one conduit into the well-bore. Oncethe conduit 102 is in place a light source 114 generates a light pulsethat is sent down the waveguides 104A-C. Each pulse of light travelsdown its respective waveguide 104A-C. The light is used to interrogateeach of the sensors 108A-N, 110A-N, 112A-N in each array 106A-C. Lightreflected back to a processor 116 is interrogated to analyze thereflected light and determine conditions at multiple locations in thewell-bore where each of the sensors 108A-N, 110A-N, 112A-N are disposed.

Embodiments described above relate to improved array temperature sensing(ATS) systems that are cane based. Benefits provided by theseembodiments include extended operating range (e.g., systems 60.0kilometers (km) in length) due to reduction in signal attenuation fromreflections at each discrete cane based sensor element within the arrayalong an optical fiber length. Interrogation of the cane based sensorelements within the ATS systems according to embodiments of theinvention enable fast (“real time”) update rates of, for example, about1.0 hertz and temperature resolution of 0.01° C., for example. As onecomparison, a Raman Distributed Temperature Sensing (DTS) typicallyoffers a maximum operating range of only 15.0 km and achieves slowerupdate rates of about 0.01 Hz and less temperature resolution at 0.1° C.

Furthermore, embodiments of the invention are substantially immune toerrors resulting from changes in differential loss between the RamanStokes and anti-Stokes bands which can occur over time due to hydrogeningress or changes in connector losses. These changes can be detrimentalto Raman DTS unlike aforementioned embodiments of the invention. Stillfurther, the cane based sensor elements within the ATS systems accordingto embodiments of the invention can be accurately located such thattemperature at a desired discrete point is measured. By an exemplarycontrast, fiber overstuff and installation procedures may preventaccurate determination of event locations along a DTS cable since thereis not necessarily a direct relation to location along the cable andposition on a DTS fiber within the DTS cable.

In addition, the cane based sensor elements within the ATS systemsaccording to embodiments of the invention can be simply packaged toisolate the cane based sensor elements from strain. In other words, thecane based sensor elements can eliminate strains applied to Bragggratings within the cane based sensor elements or at least preventstrains sufficient to induce a detectable response change in the Bragggratings from being imparted thereto.

As previously described, embodiments of the invention include the canebased sensor elements that are plated with metals for protection fromgas and/or liquid ingress. By contrast with completely fiber basedsensors and sensing systems that cannot effectively be plated withoutcreating additional complications, this plating of the cane based sensorelements does not introduce hysterisis problems and presentssubstantially no settling. With respect to settling, plating the canebased sensor elements does not alter, or at least substantially does notalter, characteristics of the Bragg gratings disposed therein after acoating process unlike more delicate fibers with less bulk that can beoverwhelmed by even a minimally thick plating and its coating process.Regarding hysterisis, the cane based sensor elements even with the metalplating provide consistent repeatable responses through temperaturecycles such as from 0.0° C. to 200.0° C. while completely fiber basedsensors and sensing systems that have been metal plated can begin to actmore like the metal coating due to stored energy absorbed by the metalcoating dominating the fiber response and detrimentally producingnon-linear changes of such configurations in response to temperature.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A method of manufacturing a sensor array for usein a wellbore, comprising: providing an optical waveguide in a firsttubing; cutting the first tubing and the waveguide to create first andsecond ends of the first tubing; sliding second and third tubing overthe first and second ends of the first tubing, respectively; positioninga tubular insert having an outer diameter less than an inner diameter ofthe second tubing into the second tubing, the tubular insert providing amount to hold the waveguide; splicing an optical sensor into thewaveguide; inserting the optical sensor into the mount; and coupling thefirst and second ends of the first tubing back together via the secondand third tubing, wherein the coupling encloses the waveguide and theoptical sensor.
 2. The method of claim 1, wherein the first tubingcomprises a metal tube.
 3. The method of claim 1, further comprisingremoving a section of the cut first tubing to create the first andsecond ends of the first tubing.
 4. The method of claim 1, wherein theoptical sensor comprises a large diameter optical waveguide having acladding surrounding a core and wherein an outer diameter of thecladding is at least 0.3 mm.
 5. The method of claim 4, wherein a ratioof the outer diameter of the cladding to an outer diameter of the coreis in a range from 30:1 to 300:1.
 6. The method of claim 1, wherein theoptical sensor comprises a Bragg grating.
 7. The method of claim 1,wherein the optical sensor has a conical tapered end and whereinsplicing the optical sensor into the waveguide comprises fusion splicingthe conical tapered end with a cut end of the waveguide.
 8. The methodof claim 1, wherein the optical sensor is metal plated.
 9. The method ofclaim 1, wherein the coupling comprises: sliding at least one of thesecond tubing or the third tubing over the tubular insert to bring thesecond and third tubing together; and securing the second tubing to atleast one of the third tubing, the first tubing, or the tubular insert.10. The method of claim 9, wherein the securing comprises at least oneof crimping, orbital welding, laser welding, or soldering.
 11. Themethod of claim 1, further comprising securing the optical sensor in themount.
 12. The method of claim 11, wherein securing the optical sensorin the mount comprises: applying silicone encapsulant into the mountbefore inserting the optical sensor into the mount; and thermally curingthe encapsulant after inserting the optical sensor into the mount. 13.The method of claim 1, wherein the mount is thermally conductive. 14.The method of claim 1, further comprising placing an armor layer aroundthe second and third tubing.
 15. The method of claim 1, furthercomprising: cutting the first tubing and the waveguide at a differentlocation to create third and fourth ends of the first tubing; slidingfourth and fifth tubing over the third and fourth ends of the firsttubing, respectively; positioning another tubular insert having an outerdiameter less than an inner diameter of the fourth tubing into thefourth tubing, the other tubular insert providing another mount to holdthe waveguide; splicing another optical sensor into the waveguide;inserting the other optical sensor into the other mount; and couplingthe third and fourth ends of the first tubing back together via thefourth and fifth tubing, wherein the coupling encloses the waveguide andthe other optical sensor.